Karbosguide.com - Module 5a2.

About adapters

Adapters

In a stationary PC, adapters are typically printed circuit
boards called expansion boards or expansion cards. They form a link between
the central PC unit and various peripherals. This is the so-called open
architecture.

Typically, adapters provide functions, which are separated from
the system board.

Adapters provide expansion capability to the PC.

There are PCs without expansion slots. In that case all functions must
be built into the system board. You could easily include chips for graphics,
ethernet, SCSI, and sound on the system board. This is not common in stationary
PCs. Portable, laptop PCs have nearly all electronics on the system
board. This is called closed architecture.

A traditional PC has a system board which contains all standard functions
(except the graphics chip). To this system board you can add various expansion
cards, which control one or more peripheral units:

The system board

Expansion boards

Standard functions
incl. control of keyboard,
COM and LPT ports. and
four EIDE units.

The integrated hard disk controller

In the Pentium based PC, the hard disk is connected to an EIDE controller,
which is integrated on the system board. Likewise, the serial and parallel
ports are connected directly to the system board. This is new. On the 386
PCs, you had to install special controller cards (I/O cards) to handle
these functions. They are included in the modern chip sets on the system
board. Other functions are not integrated. That includes:

The video controller

You have to install a video card to make the PC function. It would
be illogical to assemble a PC without a video card. You would not be able
to see what you are doing, since the video card governs data transmission
to the monitor.

The advantage of this design is, that the user can choose between numerous
video cards in various qualities. A discount store may offer a complete
Pentium based PC (without printer) and with the cheapest video card
for $669.-. If the buyer is quality oriented, he would want to spend an
additional $40 to get a much better video card.

The modular PC design

In this way, various expansion boards provide flexibility in assembling
a customized PC. At the same time, various electronics manufacturers are
specializing their production:

ASUS and Tyan are good at making system boards. Others, like S3, Matrox,
and ATI specialize in making graphics chips and expansion boards. Olicom
make only net boards. Adaptec make only SCSI controllers and Creative Labs
make SoundBlaster sound boards.

This variety of manufacturers offers the consumer wide choices. Your
PC can be customized and configured according to your needs and wallet
size.

About the electronics

The adapter is a printed circuit board. They have an edge connector,
so they can be inserted in expansion slots in the system board. The expansion
slots connect to the I/O buses. Since the Pentium system board has two
I/O buses, it has two types of expansion slots:

ISA slots

PCI slots

Typically, on a regular Pentium system board there are three or four of
each type. That gives a total of 7 expansion slots. One expansion board
can be installed in each of these. You simply press the edge connector
of the expansion board into the expansion slot. Now it is connected to
the bus.

Here you see two PCI slots open for video cards, network controllers
and others:

Below, you see a network adapter. It is an ethernet card with
PCI interface, so it fits in a PCI slot in the Pentium. This inexpensive
board allows your computer to join a network with other net board equipped
PCs. Please compare the edge connector at the button of the card with the
sockets above. They fit together!